Refining process, including regeneration of alkaline treating agents



June 4, 1957 Sour Hydrocarbons H 8 Re I Disulfide Removal I I l v Regeneration with Epoxide I (ll!) C. H. BROOKS REFINING PROCESS INCLUDING REGENERATION OF ALKALINE TREATING AGENTS I Filed May 9, 1955 F. Sour Hydrocarbons e I Electrolytic Regeneration Disulfide Removal Aqueous NaOH Aqueous NaOH R S H Removal Sour Hydrocarbons Regeneration with Epoxide I Regeneration with Epoxide Regenerated NaOH Sweetened Hydrocarbons IElectrolytic Regenerationl Disulfides RSH Removal I I Electrolytic Regeneration I I Disulfide Removal I Regeneration with Epoxide I CHARLES H. BROOKS ATTORNEY United;

:itates REFINING PRGCESS, INCLUDENG REGENERA- .TION. QF ALKALENE 'IREA'HNG AGENTS Thistinvention relates to the regeneration of alkaline treatingagents containing alkali metal mercaptides or inorganic sulfides. i

:It is known in the art to electrolytically regenerate caustic soda which has -been ilsed in. the treatment .of mineral oil fractions. Such regeneration rnaybeaccom- .plished by passing the used caustic soda through an electrolytic cell to which electric currentis supplied at a suitable voltage. The 'water inthe caustic soda is electrolyzed, oxygen and hydrogen being thereby.formed. Theoxygen reacts with the sodium mercaptides to form disulfides, oriwithsodium sulfide to form free sulfur or other products. The disulfides can be subsequently separated from the caustic soda, for example by extraction with naphtha. In the subsequent discussion, reduction in mercaptide content will be discussed, though his to be understood that the invention-also applies to reductionin inorganic sulfide content. '7

Electrolytic regeneration provides an advantageous reduction in mercaptide content of used caustic soda, but has thedisadvant-age that the 'amount'of electricity required to reduce the mercaptide content by a given increment increases as the mercaptide content decreases, so that it may not be feasible to remove a'smuch of: the mercaptide content of the used caustic as desired without encountering the necessity of using excessive amounts of electricity. The present invention provides a manner in which-large reductions in mercaptide content can be obtained without using excessive amounts of electricity.

According to the present invention, us'ed caustic is first partially regenerated electrolytically, then contacted with an epoxide reagent to react with mencaptides remaining in the caustic after the electrolytic regeneration. The treatment with epoXide eiiiciently reduces mercaptide content at levels of initial mercaptide content which are too low to permit eflicient oxidation by electrolytic oxygen. The invention thus permits electrolytic regeneration.=to be used at the-higherlevels of initial mercaptide content, at which the electrolytic regenerationis satisfactori'ly eflicient, while using epoxide treatment subsequently when the 'mercaptide content islower. {The process of the invention can be "applied to usedalkaline treating agents which contain inorganic sulfide, mercapt ides, orboth; l

hetelectrolytic regeneration can be conducted according to anyoflthe known proceduresfor such regeneration. Thus, for example, .the procedures disclosed in United StatesPatent .No. 2,654,706, issuedOctober 6, .1953, to Peter-I. Gaylor canbe employed. Any of the known methods of separating disulfides from the regenerated treating agent can be employed.

The epoxide regeneration is performed by contacting the lusedtreating agent .with' an epoxide capable of reacting with the'mercaptides and sulfides injthe treating agent. The temperature may be ordinary r oom temperaturelor higher or-.lowerttemperatures, e. g. 30 F to 300 F. Preferred epoxides .are .those having .the formula 4 i i RI! RI/I Z LE Z I atent 'ice where R is selected from the group consisting of hydrogen, halogen radicals, hydrocarbon radicals having 1 to 5 carbon atoms, phenoxyalkyl radicals having 7 to l0 carbon atoms, alkoxyalkyl radicalshaving 2 tolO carbon atoms, and

CH2CH radicals, and where 11, R" and R' are each selected from the group consisting of hydrogen, hydrocarbon radicals having 1 to 5 carbon atoms, and halogen radicals. More preferred epoxides are those having the torrnul a O RCZEtEHz where-R is selected from the group consisting of=hydrogen and alkyl radicals having 1 to 2 carbon .atoms.

xamples of suitable. epoxidesare ethylene. oxide, propylene oxide, butylene oxide,..styrene oXide,.p"nenoigy propylene oxide, butoxy propylene oxide, epichlorohydrin, butadiene oxide, etc.

The alkaline treating agent can have been used to refine "any ofvarious petroleum materials, e. g. crude oil, reduced crude, -kerosene, spirits, gasoline,'gas oil,-furnace oil, diesel'fueL-jet fuel,-lubricating oil, natural gas, refinery .gas, liquefied petroleumaga scs, etc., and maycontaint materials such as ,lphenolate s and 'naphthenates in addition. to .rnercaptides or inorganic, sulfides.

fiPre'ferably, according to the 'invention,,the electrolytic regeneration brings about inore than half of theltotal reductiondn ,m-ercaptide content obtained bythe combination of electrolytic and epoxide regeneration. lylore preferably, the electrolytic regeneration brings about mor nthreeu h o the tota edu on me captide content. Theelectrolytic regenerationvin some ta 'ce work w t sfa t ry .fi q ;Y,n, nearly all-o t c pt dc co tha b en mina fl tle vi l only a small amount, e. 1 tolO weight percent of ri ina m dcg sn s n p l t lit removed by epoxidev treating. I i

In one embodimentof the invention, used caustic soda containing mercaptides faridhiridrganic .Jsulfides -is oni e i l t e' Q id t fs e 'r aeti mate wit rgan u fi e me c d b i le Y th sa tis whichis then electrolytically regeneratedto rernoite part of the remaining mereaptides; the resulting icausticf is again contactedwith an epoxide to remove at -lea st part of ,the mercaptides rem aining aiter the electrolytic regeneration? This operation has the advantages tlfat inargariie-s'uifiaesare removed prior to thefelectrolytic regeneration films "avoiding possible in efi cts train" electrolytic action on the sulfides to produce sulfates and other uhdesirable'productsgand that electrolytic action is used 5 remove part of the mercaptides under circumstanees which produce satisfactory efficiency of removal, epoiride being used thereafter to remove mercaptides under cirfcumstances which wonld not preauesau a wi-gincie ncy in a n ielectrlolyti c regeneration. V

Th re t gn. p axi l wii fai s a q t ns P2??- captide s and ino ganicjsplfides eanhe ade seleetiye with rgard to inorganiesulfides. gllhugbyllimiting the ent of reaction of lepoxide .Wlth ,tnate'rials in the eaustic, the aniountof inorganicsulfide reacted relative totthe nt pi ts-add ea te s be max mi ed :iQ a it a t s the ext n o cn in lud i ma amo n :O epoxide, shortflregating tunes, ,low,temperatures, ,etc. :In the :light of the present specification, a; person slgilled in the art canchoose suitableconditions.

In. theep oxide .regeneratiouof treating agents containing alkali metal .sulfides. and lmercaptides, theufollowing ceeds slightly more readily than Reaction No. 3.

represent the principal reactions, ethylene oxide being the epoxide for purpose of illustration:

v NaSCHzCHzOH (hydroxyethyl mercaptide) NaOH I N8SCH2CHzOH CHgCHg H2O HO CHZCHtSCHtCHZOH (diethanol sulfite) NaOH RSNa CHzCHz H O RSCHZCHzOH (hydroxyethyl thioether) N'aOH Thus the products obtained include dihydrocarbon disulfides, diethanol disulfide, and monoethanol monohydrocarbon disulfides. The dihydrocarbon disulfides are the least soluble in the caustic and therefore the most readily recoverable therefrom, e. g. by extraction with a hydrocarbon solvent. The diethanol disulfide is the most soluble in the caustic and can advantageously be left therein to function as a solutizer in subsequent use of the caustic to remove mercaptans from the hydrocarbons. The monoethanol monohydrocarbon disulfides are intermediate in solubility; they as Well as the dihydrocarbon disulfides can be removed from the caustic, or they can be left in the caustic if desired.

The invention will be further described with reference to the attached drawing. Figure 1 illustrates a combined electrolytic and epoxide regeneration according to the invention and Figure 2 illustrates a process wherein two treating stages are employed, with epoxide regeneration of the alkaline treating agent after the first stage and a combined electrolytic and epoxide regeneration after the second stage.

In'Figure 1, sour hydrocarbons, e. g. HzS-free straight run gasoline containing mercaptans, are introduced into mercaptan removal zone 10 where they are contacted with an aqueous solution of caustic soda. The strength of the caustic and the treating conditions can be those which are used in conventional caustic treating for mercaptan removal. The used caustic containing sodium mercaptides is electrolytically partially regenerated in zone 11, the conditions being chosen to effect only partial reduction of the mercaptide content of the caustic. Disulfides formed during the electrolytic regeneration are removed according to conventional procedure in disulfide removal zone 12. The partially regenerated caustic is then contacted with an epoxide, e. g. ethylene oxide, in zone 13 in order to react the epoxide with mercaptides remaining in the caustic after the electrolytic regeneration. The reaction may be carried out for example at room temperature with agitation followed by standing for one hour. 1 to moles of epoxide per mole of mercaptides may be employed for example, and preferably at least 1.5 moles. The regenerated caustic soda containing hydroxythioether reaction products is withdrawn from zone 13 and can be used to contact additional sour hydrocarbons. If desired hydroxythioethers can be extracted from the caustic before such use by means of a hydrocarbon solvent, e. g. petroleum naphtha, pentane, etc.

The electrolytic and epoxide regeneratious combine to produce a reduction in mercaptide content to a suitable level, the efiiciency of the reduction being greater than that which could be obtained with electrolytic regeneration alone to that level.

In another embodiment, where for example the hydrocarbons contain HzS as well as mercaptans, instead of directly introducing used caustic from zone 10 through line 15 into electrolytic regeneration zone 11, the used caustic can be introduced through line 16 into epoxide regeneration zone 14 where it is partially regenerated by contact with an epoxide, e. g. ethylene oxide. The amount of epoxide used is generally within the approximate range from 1,to 5 moles of epoxide per mole of inorganic sulfide in the caustic. If substantially complete removal of inorganic sulfide from the caustic is desired, the amount of epoxide is preferably at least 1.5 moles per mole of inorganic sulfide. If conversion of inorganic sulfide to dialkanol sulfide is desired, the

amount of epoxide is preferably at least 3 moles per mole of inorganic sulfide. If minimization of mercaptide reaction with epoxide is desired, the amount of epoxide is preferably not greater than 2, more preferably not greater than 1.5 moles of epoxide per mole of inorganic sulfide. The above proportions apply generally to epoxides having only one epoxy group; epoxides having more than one epoxy group can be used in correspondingly less amounts. The amount of epoxide to be used to achieve a given purpose may vary depending on the other conditions; e. g. short contacting times, low temperatures, etc. are factors which, like small amounts of epoxide, tend to limit the extent of reaction of epoxide with constituents of the caustic.

The caustic from zone 14 is introduced through line 17 into electrolytic regeneration zone 11. From this point on, the procedure is generally the same as in the previously described embodiment.

In Figure 2, sour hydrocarbons, e. g. straight run gasoline containing both mercaptans and hydrogen sulfide, are introduced into hydrogen sulfide removal zone 20 where they are contacted with an aqueous solution of caustic soda under conditions producing removal of hydrogen sulfide, the removal of mercaptans being minimized. In the light of the present specification, a person skilled in the art can select the conditions to obtain this result, the reaction of sodium hydroxide with hydrogen sulfide occurring more readily than that of sodium hydroxide with mercaptans.

The used caustic containing sodium sulfide is contacted in zone 21 with an epoxide, e. g. ethylene oxide, the contacting being performed for example at room tempera- V ture with agitation followed by standing for one hour. Three moles of ethylene oxide per mole of sodium sulfide may be employed for example, in order to convert sodium sulfide to diethanol sulfide.

The regenerated caustic containing the diethanol sulfide formed in the regeneration is passed through lines 26 and 27 and used in zone 22 to treat the sour hydrocarbons from which hydrogen sulfide was removed in zone '20. The diethanol sulfide acts as a solutizer to increase 'the solubility of mercaptans in the caustic. Caustic containing sodium mercaptides is passed from zone 22 to zone 23 where it is electrolytically partially regenerated to convert mercaptides to disulfides, the latter being removed in disulfide removal zone 24. The caustic is then contacted with an epoxide, e. g. ethylene oxide, in zone 25 to react with mercaptides remaining after the electrolytic regeneration. The conditions in the regeneration in zone 25 can be, for example, generally the same as those in the regeneration in zone 13 of Figure 1.

If the epoxide-regenerated caustic from zone 21 contains hydroxyethyl mercaptides as well as diethanol sul-' fide, the hydroxyethyl mercaptides undergo, during electrolytic regeneration, Reactions S and 6 as set forth earlier in the specification.

Instead of removing mainly HzSin zone 20, removal oil-12S andspartial removal of-mercaptans can be efiected in'zone 20, and caustic containing sodium sulfide and mercaptides recycledthrough lines-31 and 28 to contact 'additional sourhydrocarbons containing hydrogen sulfide and mercaptans. The presence of mercaptides ,in the caustic greatly inhibits removalof mercaptans fromthe .sourhydrocarbons in the caustic, but highly effective removal of. hydrogen sulfide can be obtained in spite of the presence ofv sodium sulfide inthe caustic. A drag stream "fromithe circulating caustic is introduced through line 29 into regeneration zone'.21 wherein it is contacted with. an

.epoxi'de,.e. g. ethyleneoxide. -Preferablyil to 5 moles of epoxide are.employed permole of sodium sulfide. More preferably, at leastfl.5 moles. of epoxide per mole of sul- .lIheepoxide treate'd caustic is electrolytically partially regenerated in zone 4% to convert part of the remaining sodium mercaptides to disulfides, the latter being removed in zone 30. The partially regenerated caustic is then contacted with an epoxide, e. g. ethylene oxide, in zone 46 to react with mercaptides remaining after the electrolytic regeneration. The caustic is then passed through lines 41 and 27 into zone 22.

Instead of returning caustic to zone 20 through line 31, all of the caustic can be regenerated in zone 21 and a portion returned to zone 20 through lines 26 and 28, a drag stream 42 being taken for electrolytic regeneration.

The caustic introduced into zone 22 through line 27 may contain diethanol sulfide, diethanol disulfide, hydrocarbon disulfides, mondhydroxy disulfides, or hydroxythioethers, or mixtures thereof, depending on the previous treatment of the caustic. Various of these materials act as solutizers to increase the solubility of mercaptans in the caustic during the treating in zone 22. Caustic containing sodium mercaptides is passed from zone 22 to electrolytic regeneration zone 23. From this point on, the procedure is generally the same as in the previously described embodiment.

In another embodiment, instead of introducing the treated hydrocarbons from zone 20 through line 43 into zone 22, the treated hydrocarbons can be withdrawn as a product through line 44, and a different sour hydrocarbon charge introduced through line 45 into zone 22. In this embodiment, the charge to zone 20 can be, for example, an essentially mercaptan-free, Has-containing hydrocarbon fraction, and the charge to zone 22 an essentially Hzs-fiee, mercaptan-containing fraction.

The following example illustrates the invention:

A 15% aqueous solution of caustic soda was used to treat straight run gasoline. Various portions of gasoline were treated with the same caustic solution with occasional intervening electrolytic partial regenerations of the solution. After the tenth portion of gasoline was treated, the caustic solution contained 384 mg. of mercaptide sulfur per liter of solution and 615 mg. of inorganic sulfides as HzS per liter. The solution was electrolytically regenerated by passing through an electrolytic cell at a rate of 70 ml. per minute, the total regeneration time being 70 minutes, the voltage 3.0, the amperage l5, and the temperature 74 F. The mercaptide sulfur content of the regenerated caustic solution was 333 mg. per;liter, andtheinorganic sulfide content as -HzS was-2 49 mg. per liter. The efliciency of the regeneration was 18 percent assuming conversion of mercaptans to disulfides and sodium sulfide ;to free sulfur.

The regenerated solution, after separation of disulfides therefrom, but without any further treatment, was pas sed again through'the electrolytic cell, the'total regeneration time being'62 minutes in'this pass, and the conditions being otherwisethe same as in the first pass. The mercaptide and sulfide contents were reduced to 224 and res ectively, the efliciency being 10 percent. In four subsequent passes through the cell, in each case after separation ofjdisulfides, the conditions being similar to those in the first two passes, the mercaptide contents were reducedto 129, 64, 26 and 19 respectively, the sulfide contents were reduced to 33, 1 6, 0 and 0 respectively, and the efficiencies were 5,2, l and 0.2 percent respectively, indicating that the cell efliciency decreases as the mercaptide level, decreases. Thefollowing table summarizes the results:

.Mercaptide sulf ur' Inorganic Sulfide as H 8 :Etficiency, Pass-No. I percent 7 Before After Before After 384 I ass 615 24s 18 333 224 249 V 100 10 .224 g 129 100 33 5 129 -64' '33 16 2 .64 26 16 0 1 According to the invention, the caustic solution is, after one or more of the above passes through the electrolytic cell, contacted with an epoxide to effect considerably more efficient reduction of mercaptide content than was obtained at the same mercaptide level in the electrolytic regeneration.

In the preceding description, electrolytic regeneration has been disclosed with reference to electrolysis in the presence of the used caustic soda which is to be regenerated. Electrolytic regeneration as contemplated herein also includes introduction of freshly prepared electrolytic oxygen into the used caustic soda, the electrolysis zone and the regeneration zone being separate but the oxygen from the electrolysis zone being introduced into the regenerating zone directly after its formation.

The invention claimed is:

1. Process for regenerating aqueous solutions of alkali metal hydroxides which have been used to treat petroleurn and which contain sulfur compounds selected from the group consisting of inorganic sulfides and mercaptides which comprises: partially regenerating such solution electrolytically; and contacting the partially regenerated solution with an epoxide, thereby to react said epo-xide with sulfur compounds remaining unconverted after the electrolytic partial regeneration.

2. Process according to claim 1 wherein a greate reduction in mercaptide content is obtained in the electrolytic regeneration than in the contacting with epoxide.

3. Process for regenerating aqueous solutions of alkali metal hydroxides which have been used to treat petroleum and which contain mercaptides and inorganic sulfides which comprises: partially regenerating such solution by contact with an epoxide, thereby to react said epoxide with inorganic sulfides; further partially regenerating the resulting solution electrolytically; and contacting the resulting solution with an epoxide, thereby to react the latter epoxide with mercaptides remaining unconverted after the electrolytic regeneration.

4. Process for refining petroleum fractions which com prises: contacting a petroleum fraction containing hydrogen sulfide with an aqueous solution of an alkali metal hydroxide; contacting the resulting solution containing alkali metal sulfide with an epoxide, thereby to react said epoxide with said alkali metal sulfide; contacting a 7 petroleumfraction containing mercaptans with the epoxide-treated solution; partially regenerating electrolytically the resulting solution containing alkali metal mercaptides;

and contacting thepartially regenerated solution with an epoxide, thereby to react said epoxide with mercaptides remaining unconverted after the electrolytic regeneration.

'5. Process according to claim 4 wherein a petroleum fraction containing hydrogen sulfide and mercaptans is the charge to the first-named contacting, and the petroleum fraction product from the first-named contacting is the charge to the third-named contacting.

6. Process for refining petroleum fractions which comprises: contacting a petroleum fraction containing hydro gen sulfide and mercaptans with an aqueous solution of an alkali metal hydroxide; regenerating the resulting solution by means of an epoxide to remove alkali metal sulfides and mercaptides therefrom; contacting a petroleum fraction containing mercaptans With the regenerated solution; partially regenerating electrolytically the resulting solution containing alkali metal mercaptides; and contacting the partially regenerated solution with an epoxide, thereby to react said epOXide with mercaptides remaining unconverted after the electrolytic partial regeneration.

7. Process for refining'petroleum fractions which comprises: contacting a petroleum fraction containing hydrogen sulfide and mercaptans with an aqueous solution of an alkali metal hydroxide; contacting the resulting solution containing alkali metal sulfide and alkali metal mercaptide with an epoxide to convert alkali metal sulfide; using the resulting treating agent to contact additional petroleum hydrocarbons containing hydrogen sulfide and mercaptans to remove hydrogen sulfide therefrom; contacting the resulting solution containing alkali metal sultide and alkali metal mercaptide with an epoxide to convert alkali metal sulfide; partially electrolytically regenerating the resulting solution to convert alkali metal mercaptides; and contacting the resulting solution With an epoxide to convert alkali metal mercaptides remaining after the electrolytic regeneration.

8. Process for refining petroleum fractions which comprises: contacting a petroleum fraction containing hydrogen sulfide and mercaptans with an aqueous solution of an alkali metal hydroxide; contacting the resulting solution containing alkali metal sulfide and alkali metal mercaptide with a petroleum fraction containing hydrogen sulfide and mercaptans to selectively remove hydrogen sulfide; contacting the resulting solution containing alkali metal sulfide and alkali metal mercaptide with an epoxide to convert alkali metal sulfide; partially electrolytically regenerating the resulting solution; and contacting the resulting solution with an epoxide to convert alkali metal mercaptide remaining after the electrolytic regeneration.

9. Process according to claim 8 wherein, after the lastnarned contacting, the resulting solution is contacted with the petroleum fraction from which hydrogen sulfide was selectively removed, thereby to remove mercaptans.

References Cited in the file of this patent UNITED STATES PATENTS 

1. PROCESS FOR REGENERATING AQUEOUS SOLUTIONS OF ALKALI METAL HYDROXIDES WHICH HAVE BEEN USED TO TREAT PETROLEUM AND WHICH CONTAIN SULFUR COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF INORGANIC SULFIDES AND MERCAPTIDES WHICH COMPRISES: PARTIALLY REGENERATING SUCH SOLUTION ELECTROLYTICALLY; AND CONTACTING THE PARTIALLY REGENERATED SOLUTION WITH AN EPOXIDE, THEREBY TO REACT SAID EPOXIDE WITH SULFUR COMPOUNDS REMAINING UNCONVERTED AFTER THE ELECTROLYTIC PARTIAL REGENERATION.
 6. PROCESS FOR REFINING PETROLEUM FRACTIONS WHICH COMPRISES: CONTACTING A PETROLEUM FRACTION CONTAINING HYDROGEN SULFIDE AND MERCAPATANS WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE; REGENERATING THE RESULTING SOLUTION BY MEANS OF AN EPOXIDE TO REMOVE THE ALKALI METAL SULFIDES AND MERCAPTIDES THEREFROM; CONTACTING A PETROLEUM FRACTION CONTAINING MERCAPTANS WITH THE REGENERATED SOLUTION; PARTIALLY REGENERATING ELECTRICALLY THE RESULTING SOLUTION CONTAINING ALKALI METAL MERCAPTIDES; AND CONTACTING THE PARTIALLY REGENERATED SOLUTION WITH AN EPOXIDE, THEREBY TO REACT SAID EPOXIDE WITH MERCAPTIDES REMAINING UNCONVERTED AFTER THE ELECTROLYTIC PARTIAL REGENERATION. 